What is introspection?

GObject introspection is a middleware layer between C libraries (using GObject) and language bindings. The C library can be scanned at compile time and generate a metadata file, in addition to the actual native C library. Then at runtime, language bindings can read this metadata and automatically provide bindings to call into the C library.

Goals

The introspection project has two major goals, and a variety of more minor ones.

Two level applications - C and <your favorite runtime>

It makes sense to build many kinds of applications using (at least) two different levels and languages. Those being C+GObject, and a managed (GC'd) runtime. C is good for graphics, multimedia, and lower level systems work. However, writing complex software is difficult and error-prone without garbage collection. A managed runtime such as JavaScript, Python, Perl, Java, Lua, .NET, Scheme etc. makes a lot of sense for non-fast-path application logic such as configuration, layout, dialogs, etc.

Note: to achieve this goal you need to write your code using GObject convention. if you don't know about gobject please see here

Thus, one of the major goals of the GObject introspection project is to be a convenient bridge between these two worlds, and allow you to choose the right tool for the job, rather than being limited inside one or the other. With the introspection project, you can write for example a ClutterActor or GtkWidget subclass in C, and then without any additional work use that class inside JavaScript.

Sharing binding infrastructure work, and making the platform even more binding-friendly

Historically in GNOME, the core platform has been relatively binding-friendly, but there are several details not captured in the C+GObject layer that bindings have needed. For example, reference counting semantics and the item type inside GList's. Up until now various language bindings such as Python, Mono, java-gnome etc. had duplicated copies of hand-maintained metadata, and this led to a situation where bindings tended to lag behind until these manual fixups were done, or were simply wrong, and your application would crash when calling a more obscure function.

The introspection project solves this by putting all of the metadata inside the GObject library itself, using annotations in the comments. This will lead to less duplicate work from binding authors, and a more reliable experience for binding consumers.

Additionally, because the introspection build process will occur inside the GObject libraries themselves, a goal is to encourage GObject authors to consider shaping their APIs to be more binding friendly from the start, rather than as an afterthought.

Additional goals and uses

API verification - Sometimes the API of a library in our stack changes by accident. Usually by a less experienced developer making a change without realizing it will break applications. Introspecting the available API in each release of the library and comparing it to the last one makes it easy to see what changed

Documentation tools - The tools written inside of the GObjectIntrospection can easily be reused to improve that problem. Essentially; replacing gtk-doc. We want to document what we export so it makes sense to glue this together with API verification mentioned above (see BindingsDocumentation)